1. Field of the Invention
The present invention generally relates to the handling and transfer of wafers typically used in the fabrication of integrated circuits and flat panel displays.
2. Description of the Prior Art
Vacuum processing systems for processing 100-mm, 200-mm, 300-mm or other diameter wafers are generally known. A typical vacuum processing system, which may also be referred to as a semiconductor manufacturing tool, has a centralized transfer chamber, or vacuum central handler, which is the center of activity for the movement of wafers being processed in the system. One or more process chambers attach to the transfer chamber at valves through which the wafers are passed by a robot in the transfer chamber. The valves are selectively opened and closed to isolate the process chambers from the transfer chamber while wafers are being processed in the process chambers. Physically, the process chambers are either supported by the transfer chamber and its platform or are supported on their own platform or platforms. Inside the system, the transfer chamber is typically held at a constant vacuum, while the process chambers may be pumped to a higher vacuum as may be required to perform the processes being carried out therein. Afterward, the chamber pressure level must be returned to that in the transfer chamber before the valve can be opened to permit access between the chambers, so that a wafer that has been processed can be removed and one to be processed can be placed therein.
Access to the transfer chamber from outside the semiconductor-manufacturing tool is typically gained through one or more load-lock chambers. The load-lock chambers cycle between the pressure level of the ambient atmosphere of the manufacturing facility, such as a clean room, and the vacuum pressure level in the transfer chamber in order for the wafers to be passed therebetween. As such, the load-lock chambers transition the wafers between the atmospheric pressure of a very clean environment to the vacuum of the transfer chamber. Load-lock chambers are designed to hold only a single wafer, or may have a sufficiently large volume to hold several wafers, for example, typically up to twenty-five wafers. In such a case, the wafers are stacked above one another in a wafer cassette with a horizontal space between each wafer to permit a robot wand to reach under a wafer to remove it for processing.
The load-lock chambers may open to the ambient environment for an operator to load a wafer cassette, or pod, thereinto or wafers may be transferred from a pod to a load lock chamber in a very clean environment at atmospheric pressure. In the latter instance, there may also be a wafer orienter or aligner at a point between the wafer pod and load lock chamber to align the wafer so that the wafer will be properly oriented in the load lock chamber.
Transfer chambers commonly have four to six facets, or sides, where process chambers and load-lock chambers can be mounted. A six-faceted, or six-sided, transfer chamber typically has load-lock chambers mounted on two facets and process chambers mounted on the other four facets. The process chambers may be, for example, rapid thermal processing (RTP) chambers, physical vapor deposition (PVD) chambers, chemical vapor deposition (CVD) chambers, etch chambers, and others. The productivity of a vacuum processing system is increased when more process chambers are mounted to the transfer chamber because more wafers can then be processed at a given time. Additionally, less space is required in the manufacturing facility to process a certain number of wafers if the productivity of the system is maximized.
Single-wafer load lock chambers present several advantages to one seeking ways to increase productivity in a wafer-processing facility. Typically, the volume of a single-wafer load-lock chamber, or load lock, is much smaller than that of one capable of holding a wafer pod. As a consequence, a single-wafer load lock can be evacuated, or pumped down, to a vacuum and vented, or restored to ambient atmospheric conditions, much more quickly than one capable of holding a wafer pod. In addition, a single-wafer load lock can be used to perform pre-heating, cool-down or other ancillary processes on the wafers to save room for other equipment in the process chambers.